1. Field of the Invention
The invention relates to an aviation turbomachine compressor, in particular a turbojet compressor, and specifically a compressor for an airplane engine. The invention relates in particular to a high pressure (HP) compressor. It is most applicable to an axial compressor. The invention also relates to a turbomachine including such a compressor.
Such a compressor, in particular when it is a compressor of high pressure type, is a critical component of a turbomachine, since it determines the stability margins of the machine and since it is subjected to high mechanical loads at high temperatures.
2. Description of the Related Art
The HP compressor of a turbojet is made up of a plurality of successive compression stages. Each stage comprises a row or grid of rotor blades (a rotor wheel) and a row or grid of stator vanes (a stator wheel).
On passing through a grid of stator vanes (stator wheel), air is subjected to deflection that causes it to lose speed. Under such conditions, aerodynamic losses occur that are due to friction, which losses are also known as diffusion losses.
During operation of the engine, the clearance that exists between the rotor wheels and the stator casing surrounding the compressor constitutes a major technological effect limiting the performance of a high pressure compressor: it deteriorates the efficiency and operability of the compressor.
Friction losses and losses due to the clearance effect may become so severe as to generate air-flow separation, thereby giving rise to a “pumping” phenomenon that constitutes a limit on the operating range over which the compressor can be used. Any device that enables the stability range of the compressor to be extended enables the performance of the compressor to be increased.
Various approaches have been proposed for minimizing those phenomena that degrade the efficiency and the operating range of a turbomachine.
Commonly, air recirculation is established by bleeding air in register with (or immediately downstream from) the tips of a row of rotor blades and then reinjecting said air upstream from the tips of the same row of rotor blades. Such air recirculation generally passes via a cavity or passage defined in the stator casing. This applies to documents US 2005/0226717 and U.S. Pat. No. 5,474,417. Such air recirculation is sometimes associated with treatments applied to the casing, as in document EP 1 413 771. Nevertheless, various problems remain that are associated therewith, in particular significant disturbance to the air stream at the location where the recycled air is injected.
In document U.S. Pat. No. 7,077,623 B2, air recirculation is established between a plurality of successive compression stages via the insides of the airfoils and via the casing carrying the airfoils, firstly along the rows of stator vanes and secondly along the rows of rotor blades. That solution is complex to implement.
Documents DE 10 2005 052466, GB 504 214, EP 0 719 908, US 2005/0226717 and NL 45 457 all provide for an air injection system including at least one air injection passage having an outlet segment that opens out in inclined manner upstream from and towards a row of rotor blades.